This invention relates to the field of electronic trigger devices, and in particular to a method and apparatus for detection of a predefined time sequence of events in a single signal, and the subsequent generation of an indication therefor.
In electronic monitoring applications, it is frequently desirable to monitor a signal for the occurrence of selected events, and produce an indication in response thereto. Monitoring activity may be performed with respect to a single signal or a plurality of signals. It is to be understood that the present invention is concerned with monitoring a single signal for the occurrence of a plurality of sequential events occurring therein, and the production of an indication in response thereto.
In the past, single signals have been monitored with respect to level and slope criteria. In particular, an indication is generated responsive to the level and slope of a monitored signal becoming equal to a selected level and slope. While such an approach is useful in a wide variety of applications, e.g., a triggered sweep oscilloscope, there are many applications where a more complex monitoring capability is necessary.
Level and slope information may be combined with other information to produce more complex trigger criteria. By way of illustration, an indication generated as a result of level and slope criteria being satsfied may be used to trigger a timing device. The timing device thereafter operates to measure a selected period of time, and produce an indication subsequent to the passage of the selected time period. Delayed trigger sweep oscilloscopes are an illustration of such an application.
While the foregoing applications have addressed detection of a single event, more complex monitoring operations may involve the detection of a series of sequential events in a single signal. By way of illustration, a plurality of events in a monitored signal may be defined by specifying a level and slope for each of such events. In addition, the amount of time by which each of such events is displaced from either an adjacent event or a final event in such a sequence may be specified. Thereafter, level and slope monitoring apparatus may be employed to detect the occurrence of each of such events, and used with associated timing apparatus to produce a trigger signal at the occurrence of a final event in such a sequence. While such an arrangement is plausible, a number of practical considerations preclude effective use of such an approach. In particular, it is frequently difficult to precisely specify the amount of time between events in such a sequence. In addition, the times at which the events occur may likewise vary. Such timing inaccuracies generally preclude successful detection of a sequence of events in a single signal.
In a similar manner, it is frequently desirable to monitor a binary signal for the occurrence of a selected pattern of information. In the past this has generally been accomplished through the use of a state machine which operates to continuously monitor a signal, and change states upon the occurrence of each change in the binary signal. Again, while such an approach in theory is possible, practical considerations frequently operate to limit the effectiveness of such an approach. In particular, as the clock which is associated with the binary signal is generally not available for synchronization purposes, timing differences between the clocks associated with monitoring apparatus and the apparatus which is producing the binary signal frequently preclude reliable detection of such a pattern of information.
There is consequently a need for electronic monitoring apparatus capable of detecting a sequence of events in a single signal, notwithstanding timing differences which may occur between the sequential events therein.